The subject of the present invention is a marking device for a mould, for injection or press moulding of parts made of synthetic substances or pressure die-cast parts.
This invention relates to the moulding of parts which need to be identified, particularly by a date of manufacture. To do this, a device is positioned in the mould.
There are in existence inserts which comprise a number of parts, which can move with respect to each other. By altering the relative position of two parts, it is possible to alter the marking to be made on the part. Thus, for example, a first part on which there is engraved an arrow and the indication of a year can rotate in an annular part bearing the numbers 1 to 12. By rotating the part placed on the inside, the arrow can point to one of the numbers engraved on the outer part. This makes it possible to indicate the month of manufacture on parts made in a mould fitted with such a marking device.
To reduce the cost of a mould, there are also marking devices which consist of just one part positioned in the mould. This part is, for example, a cylindrical part placed in a housing of a complementary shape. This part, generally of circular cross section, is fitted tightly in its housing, in order to prevent any relative movement between the marking device and the wall of the mould.
However, these marking devices bear an indication that the manufacturer may need to modify. This may, for example, be the indication of a year, or a symbol liable to change (product mark, customer reference, etc.).
The drawback of these marking devices is that it is difficult to change them. They are not easy to remove and this removal generally leads to damage preventing the marking device from being reused, or even destroying it. Indeed it is not uncommon for it to be necessary to make a hole in the marking device in order to be able to extract it from its housing.
This takes a great deal of time. Furthermore, when a hole is drilled, chips are produced and these run the risk of falling into the mould. Finally, there is the risk of damaging the mould.
Document JP 63 013 724 describes a method for indicating a date of moulding on a part made of synthetic material in a mould. This method consists of using a mould which has moulding dates and two different types of screws, and then placing a predetermined type of screw opposite a part of the mould corresponding to the date that is to be shown.
The object of the invention is therefore to provide a simple marking device intended to have a fixed position in a mould, but which can be readily removed and refitted.
To this end, it proposes a marking device which comprises:
a head intended to lie flush with the internal face of the wall of the mould, that face of the head that faces towards the inside of the mould having a marking and means allowing the head to be turned,
a threaded cylindrical body forming a single piece with the head of the device.
This marking device can be screwed directly into the interior wall of the mould, such that the head lies flush with this wall. The wall of the mould then has a tapped hole, the shape of which corresponds to the shape of the device. To change the marking made on the parts manufactured in the mould, all that is required is for the marking device to be unscrewed and another marking device of the same shape but with the desired marking to be screwed back in in its place.
If the wall of the mould already has a housing for housing a marking device, it is possible to insert into this housing a part which matches the shape thereof, and to make in this intermediate part a tapped hole to allow the marking device according to the invention to be housed.
Advantageously, the marking device has a head of circular cylindrical shape, with an outside diameter that is greater than the outside diameter of the body. It is then possible to achieve a tight fit between the head of the marking device and the wall of the mould, at the peripheral surface of the head.
In this last instance, a part of frustoconical shape preferably connects the head of the device to its body, so as to obtain a better fit of the device in its housing.
In instances where the wall of the mould does not have a tapped hole, but only has a housing of circular cylindrical shape, the marking device further comprises a tapped bush, the outside diameter of which corresponds to the outside diameter of the head of the device, and the tapping of which corresponds to the screw thread of its body, so that when the body is screwed into the bush, the entity thus formed is of circular cylindrical shape. This assembly can then sit in the wall of the mould. Of course, the outside diameter of the bush and of the head will be adapted to suit the inside diameter of the housing in the wall of the mould.
For the marking devices according to the invention and described hereinabove, the means for turning the head are advantageously a straight slot passing through the centre of that face that faces towards the inside of the mould. However, it may be any other means such as, for example, a hexagonal cylindrical recess or a square shape in relief.
In any case, the invention will be clearly understood from the description which follows, with reference to the appended diagrammatic drawing which depicts, by way of non-limiting examples, two embodiments of a marking device according to the invention.